1. Field
These inventions relate to apparatus, for example ballasts, and methods for operating ballasts, and apparatus and methods for operating fluorescent and similar light sources, for example, ballasts, inverters, drivers, or oscillators for operating such light sources.
2. Related Art
Electronic ballasts are widely used to power lighting circuits, including conventional fluorescent lamps, compact fluorescent lamps, and other fluorescent lighting components. Some electronic ballasts have power factor correction while others do not. In some ballasts, passive power factor correction can be accomplished using a large inductor in series with the power line input. Active power factor correction can be applied in other ballasts using a boost circuit. In other ballasts having no power factor correction, the ballasts are generally considered to have normal power factor. Examples of ballasts are shown in U.S. Pat. No. 6,008,589, incorporated herein by reference.
In electronic ballasts having normal power factor, such ballasts are not generally capable of operating over a wide range of voltages. However, ballasts having active power factor correction generally have low total harmonic distortion but are more expensive than normal power factor ballasts, which have higher total harmonic distortion. Active power factor correction ballasts, because of their lower total harmonic distortion can be easily used in both consumer and industrial power applications where input voltages can range widely from 120 volts to 277 volts. Such ballasts can have wide applicability with low total harmonic distortion. However, normal power factor ballasts are not easily used over a number of different voltages without high total harmonic distortion.
Ballasts used in large installations having a large number of light units preferably have good power factor correction. Without good power factor correction, excessive harmonic distortion in the line current can lead to overheating of the neutral conductor in a facility using three phase power. In areas where power utilities monitor or meter the power factor of customers, especially big consumers, the utilities may charge rates that may increase when the power factor is low. In other situations, normal power factor ballasts may be desirable, such as those where there is a relatively small number of lighting units or where the input voltage levels are well-known or relatively reliable. For example, vending machine lights, UV sterilization lights, and advertising displays use a relatively small number of lighting units It is still desirable for these ballasts to be able to operate at two voltages, even though they do not need high quality power factor correction. Additionally, portable or mobile facilities such as command posts, field hospitals, aid stations and the like operate on portable generators, many capable of operating at either 120 volts or 240 volts. For lighting systems intended to operate only at 120 volts, inadvertent application of 240 volts through an incorrect setting at the generator may quickly destroy the lighting units and possibly other equipment used in the facilities. Therefore, such lighting units would quickly fail if they could not operate at both 120 volts and 240 volts or 277 volts, an industrial voltage level.
In some commercial applications, it is not always confirmed whether the facility operates at high voltage such as 240 or 277 volts or off 120 volts. If the lighting unit operates at only one voltage level, the lighting unit is quickly destroyed or may be ineffective if the supply voltage is a different level.